> Most system calls taking flags first check that the flags passed in are> valid, and that helps userspace to detect when new flags are supported.> > But swapon never did so: start checking now, to help if we ever want to> support more swap_flags in future.> > It's difficult to get stray bits set in an int, and swapon is not widely> used, so this is most unlikely to break any userspace; but we can just> revert if it turns out to do so.

It would be safer to emit a nasty message then let the swapon proceedas before.